Operating system? 32 bit? 64 bit? We run JBoss on multi-server configurations often, using SpecJAppServer benchmark as the test bed. But we also have some other hand-coded tests. One of the things you will find is that an app server will not scale beyond 4 CPUs. This applies to any app server, not just to JBoss. In fact, you should affinitize the app server to 2, 3 or 4 of your CPUs - the actual number depends on your application (try each one, pick the best), and preferrably CPUs that occupy a common bus (usually 4 CPUs share a bus). Regarding Xmx/s, on a 32-bit system we have not been able to go over 1.7 GB of heap, on a 64-bit system only RAM is the limit (though with a really large heap you get really long pause times during a major collection. Also see http://wiki.jboss.org/wiki/Wiki.jsp?page=SPECjAppServer2002Tuning for some heap tuning hints. Specifically http://wiki.jboss.org/wiki/Wiki.jsp?page=SPECjAppServer2002TuningComponen... This wiki entry contains most of what we learned running on large-scale systems. View the original post : http://www.jboss.com/index.html?module=bb&op=viewtopic&p=4053149#... Reply to the post : http://www.jboss.com/index.html?module=bb&op=posting&mode=reply&a...